Interleukins, interferons, colony stimulating factors and TNFα are examples of a group of diverse multi-functional proteins called cytokines. Cytokines are a class of secreted soluble proteins normally present in very low concentration in a variety of cells. Lymphoid, inflammatory hemopoietic and other cells such as connective tissue cells (e.g. fibroblasts, osteoblasts) secrete a variety of cytokines which regulate the immune, inflammatory, repair and acute phase responses by controlling cell proliferation, differentiation and effector functions. The effects of cytokines are mediated through binding to high affinity receptors on specific cell types.
An important cytokine is IL-10, a 35-40 kDa peptide produced by helper T-cells, B-cells, monocytes, macrophages and other cell types. In vitro, IL-10 has demonstrated immunosuppressive properties as evidenced by its ability to suppress cytokine production including IL-1 and TNFα.
IL-10 also inhibits activation of other inflammatory cytokines, and therefore has potent anti-inflammatory activity.
It has been of recent interest to administer IL-10 in the treatment of certain conditions characterized by excessive IL-1 and TNFα production. Such diseases or conditions include loosening of prosthetic joint implants, inflammation, diabetes, cancer, graft versus host diseases, viral, fungal and bacterial infections, lipopolysaccharide endotoxin shock, diseases of depressed bone marrow function, thrombocytopenia, osteoporosis, spondyloarthropathies, Paget's disease, inflammatory bowel disease, arthritis, osteoarthritis, autoimmune diseases such as rheumatoid arthritis, systemic lupus erythematosus, and connective tissue diseases.
For example, purified IL-10 has been shown in vitro to suppress certain types of viral infections. U.S. Pat. No. 5,665,345 discloses a method for inhibiting replication of the human immunodeficiency virus, retro-viruses, and Kaposi sarcoma in human cells by administering IL-10.
IL-10 has also been suggested for use in the treatment of certain cancers. U.S. Pat. No. 5,570,190 discloses administering exogenous IL-10 to treat mammals suffering from acute myelogenous leukemia and acute lymphocytic leukemia. IL-10 is said to be administered either in the purified or recombinant form and is believed to inhibit the proliferation of acute leukemia blast cells.
Similarly, IL-10 was shown to inhibit bone marrow metastasis in severe combined immunodeficient mice.
The above conventional approaches to treating conditions characterized by excessive IL-1 and TNFα production have been limited to administering exogenous purified or recombinant IL-10 intravenously. Since IL-10 is a protein, it is difficult to infuse intravenously into a mammal because proteins often leach out of solution and bind to the plastic or glass used in intravenous administration sets. Also, proteins are often incompatible and precipitate when mixed with physiological solutions such as dextrose or saline. In addition, oral and topical routes are unavailable for IL-10 administration. The oral route is unavailable because protein is degraded in the gastrointestinal tract.
None of the above approaches suggests enhancing endogenous IL-10 production in mammals for prophylaxis and treatment of diseases or conditions.
Further, it is known that IL-10 is a powerful deactivator of macrophages and T cells, and inadequate production has been implicated in various autoimmune and inflammatory disorders.